freebsd vs linux: performance problem

Shantanu Ghosh shantanu_ghosh at
Thu Dec 13 20:24:33 PST 2007

--- Erich Dollansky <oceanare at> wrote:

> Hi,
> Shantanu Ghosh wrote:
> > --- Erich Dollansky <oceanare at> wrote:
> > 
> >> Don't you call memcpy?
> > 
> > Well, I first did - then I wrote a function to do the same, just to
> > make sure that the code executed is exactly the same in both the
> cases.
> > The difference was there both when using memcpy, and when using the
> > replacement function.
> Do you have Linux compatibility installed on the FreeBSD machine?
> You should then be able to run the Linux binary to see what happens
> then.
> I have had once the problem of a task moving from CPU to CPU and s 
> performing badly on FreeBSD.
> I am not informed how this is handled currently.

This could be something I am facing. I noticed that when I run vmstat
while running this code, on linux, there's hardly any perceptible
difference in the number of context switches, but on freebsd, the
number of context switches in the system seems to go up a bit. However,
this is not very reliable.

Do you know how I can check this migration?

> I also assume that this example is a single-threaded program which 
> should perform just fine on single CPU machine.
> One other thing, can you just boot up with one CPU and one core to
> see 
> what happens then?

While I have not tried it on this machine, on a single cpu machine, the
non-SMP build of freebsd seems to perform as well as linux for this
kind of test.

Thanks a lot for your help.
> Erich
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